Engine combustion using gasoline fuel may generate particulate matter (PM) (such as soot and aerosols) that may be exhausted to the atmosphere. To enable emissions compliance, particulate filters (PF) may be included in the engine exhaust, to filter out exhaust PMs before releasing the exhaust to the atmosphere. Such devices may be periodically or opportunistically regenerated during operation of an engine to decrease the amount of trapped PM. However, a portion of the trapped PM may not burn during PF regeneration due to the geometry of the PF and/or location of the PF and accumulation of such unburnt PM may result in increased exhaust back pressure resulting in decreased engine efficiency. Also, conditions for PF regeneration may not be available during prolonged periods of vehicle operation, causing PF load to keep accumulating.
Various approaches are provided for cleaning a PF in response to PM loading reaching a threshold amount. In one example, as shown in U.S. Pat. No. 5,725,618, Shimoda et al. discloses a method to backwash a particulate filter coupled to an exhaust passage of a diesel engine. Pressurized air from an air chamber may be routed from downstream of the PF to upstream of the PF to generate a pressure for removal of the PM accumulated on the PF. The pressurized air containing the soot is then routes to a PM burning section, wherein the PM is burnt using electrical energy from a heater coupled to the burning section.
However, the inventors herein have recognized potential disadvantages with the above approach. As one example, additional components may be required to remove the accumulated soot from the PF and then to burn the soot, leading to increased cost. By using electrical energy from a separate heater to burn the soot, parasitic loss of engine power may increase. Also, backwashing PF during engine operation may result in soot entering the combustion chambers via the exhaust valve, thereby adversely affecting combustion stability. Further, engine operation with an increased exhaust temperature may adversely affect emissions quality.
In one example, the issues described above may be addressed by a method comprising: routing exhaust gases from an engine through a particulate filter (PF), and responsive to a higher than threshold exhaust particulate filter (PF) soot load and when the engine is no longer combusting, flowing ambient air through the PF and then routing the ambient air with soot collected from the PF to an intake manifold to deposit the soot on an air filter coupled to the intake manifold. In this way, during vehicle key-off, by opportunistically reverse rotating either an exhaust turbine of a turbocharger, or the engine, air may be routed via the PF in a reverse direction to remove soot accumulated on the PF and then to deposit the soot on the intake air filter to be subsequently routed to the engine cylinders for combustion.
As one example, during a vehicle key-off condition, in response to a higher than threshold PF soot load and a lower than threshold exhaust temperature, the controller may carry out a cleaning routine for the PF. A turbocharger including an exhaust turbine and an intake compressor may be rotated in a reverse direction via an electric motor coupled to the turbine. In response to the reverse rotation of the exhaust turbine, ambient air may enter the exhaust passage from the tailpipe and flow to the turbine via the PF. As the ambient air flows through the PF in a reserve direction (from downstream of the PF proximal to the tailpipe to upstream of the PF proximal to the turbine), soot accumulated on the PF may be removed with the air flow. The wastegate may be closed and an exhaust gas recirculation (EGR) valve coupled to a higher pressure EGR (HP-EGR) passage may be fully opened to route the ambient air with soot from downstream of the turbine to upstream of the intake compressor (proximal to the charge air cooler) via the turbine and the HP-EGR passage. The air with the soot may then be routed to upstream of the intake compressor (proximal to the intake air filter) via one of the compressor and a compressor recirculation passage. The air may then flow out of the intake passage to the atmosphere via the intake air filter, depositing the soot on the intake air filter and removing any particulate matter deposited on the intake filter. For a hybrid electric vehicle (HEV), during a vehicle key-off condition, in response to a higher than threshold PF soot load and a lower than threshold exhaust temperature, the engine may be reverse rotated using motor torque from an electric machine. Due to reverse rotation of engine, ambient air may enter via the tailpipe and while flowing through the PF may remove the accumulated soot. The air with the soot may then be routed to the intake air filter via the turbine, the engine cylinders, and the compressor recirculation passage. During an immediately subsequent engine start, the soot deposited on the intake air filter may be routed to the engine cylinders (for combustion) along with the intake air flow.
In this way, by leveraging an existing turbocharger or a HEV electric machine to clean the soot load deposited on a PF, the cost associated with adding supplemental engine components to be used for soot removal may be reduced. By cleaning the PF during vehicle key-off, the cleaning routine may be carried out opportunistically even during prolonged periods of vehicle operation without fulfillment of PF regenerating conditions. The technical effect of flowing air out of the intake passage via the intake air filter is that particulate matter deposited on the intake air filter may so be removed with the air flow, thereby allowing cleaning of both the PF and the intake air filter with the same air flow. By routing the soot to the engine cylinders for burning, exhaust temperature may not be increased during engine operation, thereby improving emissions quality, engine performance, and fuel economy.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.